The goals of the proposal are 1)to examine how variation in a frustration event affects infants' negative emotions, physiological responses, and behavior, 2) to observe whether infants' response to frustration at 6 months is related to their frustration at three years, and 3) to examine whether maternal responsivity to child's emotion at 18 months mediates this relation. These questions will be addresses in two separate studies. Both use contingency learning/frustration procedures which allow simultaneous assessment of infants; arm activity, facial expressions, cortisol reactivity, and heart rate. Study 1 will vary two aspects of expectancy that define contingency, examining the influence of their violation infants' emotions, cardiac regulation as measured by vagal tone, and arm activity. Six-month-old infants (N=200) will be trained to expect that their pulling on a string in a pleasant event. A brief frustration period allows observation of infant responses when probability-specified aspects of contingency will be violated, using a model of contingency probabilities developed by Watson (1885) and others. Infants will be randomly assigned to groups which will experience either reduced predictability or reduced controllability. Group differences observed during this phase will show how various forms of expectancy violation affect infants' instrumental arm activity, facial expressions, and physiological regulation may be shaped by environmental contingencies, and their disruption. In Study 2, arm activity, emotion expression, and cardiac regulation as measured by vagal tone will be observed in infants(N=150) and related to later frustration. Infants will be seen in the contingency/frustration paradigm at 6 months of age and individual differences will be related to children's behavioral and cardiac responses to challenging tasks and games when they are 3 years of age. Maternal responsivity of toddler emotion will be observed at 18 months. The results are expected to lead to the identification of children who are prone to frustrated anger and who may be at risk for behavioral difficulties based on their reactivity, as well as their maternal response to that reactivity.